Transformer with connector and method of assembly

ABSTRACT

A connector assembly for the low voltage, aluminum, output conductors of a transformer which includes a copper stud forming the through connection from the interior of a transformer casing to the external connector. The low voltage leads from the transformer assembly are preferably formed of aluminum and are attached to the copper stud by means of a concentrically grooved brass washer which is forced into the face of dead-soft aluminum strip by means of a compression nut. The electrical path for the connector assembly includes the dead-soft aluminum strip, the concentrically grooved brass washer, the brass compression nuts and the copper stud.

United States Patent [1 1 Mallet 336/58 Fisher June 19, 1973 UNTRANSFORMER WITH CONNECTOR AND METHOD OF ASSEMBLY Primary Examiner-E. A.Goldberg Attorney-J. King Harness, Paul F. Seibold, Cyrus [75] Inventor.John L. Fisher, Lexington, Ky. G- Minkler [73] Assignee: KuhlmanCorporation, Troy, Mich. H i V 22 Filed: Nov. 4, 1971 [57] ABSTRACT Aconnector assembly for the low voltage, aluminum, [21] l95748 outputconductors of a transformer which includes a copper stud forming thethrough connection from the i [52] US. Cl. 336/192, 29/602, 336/58,interior of a transformer casing to the external connec- 339/595 A tor.The low voltage leads from the transformer assem- [51] Int. Cl. H0lf15/10 bly are preferably formed of aluminum and are at- [58] Field ofSearch 336/192, 58; tached to the copper stud by means of aconcentrically 339/95 A; 29/602 grooved brass washer which is forcedinto the face of dead-soft aluminum strip by means of a compression [56]References Cited nut. The electrical path for the connector assembly in-UNTTED STATES PATENTS cludes the dead-soft aluminum strip, theconcentrically 728 092 5 1903 Edwards ...Q.'. 339 95 A brass wash, thebrass i l 2,990,528 6 1961 Zimsky 336/58 the copper 3,314,030 4/1967 22Claims, 8 Drawing Figures TRANSFORMER-WITH CONNECTOR AND METHOD OFASSEMBLY BACKGROUND AND SUMMARY OF THE DEVELOPMENT This inventionrelates generally to a connector assembly for connecting aluminum stripconductors to a stud and more particularly to a connector assembly whichincludes a concentrically grooved washer made of material which issufficiently hard relative to the aluminum conductor that the aluminumconductor will flow into the voids created by the concentric groovesthereby eliminating poor connections inherent in thermally cycledconnectors for aluminum strips.

In the past, copper was the common material utilized for transformersecondary coil leads or busses, the copper being typically formed in arelatively flat strip. However, with the unusual increase in cost ofcopper, other materials have been sought which have the properelectrical and mechanical characteristics for use in connection with theleads of the secondary winding of a transformer.

One material which hasbeen found to have the desirable electricalcharacteristics is aluminum. Typically, electrical grade aluminum isextremely soft and attains its highest conductivity in the dead-soft,annealed state. However, certain problems have arisen in the use ofaluminum for the secondary strip lead, these problems having beenpresent form some period of time.

For-example, one problem which has existed with the use of dead-softaluminum is the tendency for the aluminum to cold flow out of theconnector assembly when any compressive force is applied. This problemparticularly arises when it is desired to clamp the aluminum strip to aconnector assembly for providing either a termination of the electricalconductor or the connection of the conductor to an external connectoroutside of the transformer casing.

The problem becomes particularly acute when the phenomenon of thermalcycling occurs wherein the thermal expansion of the various componentsof the connector assembly are different, thus creating an extremely highcompressive force on the strip aluminum.

cled.

For example, aluminum expands at a rate which is approximately 1.3 to1.5 times the rate of expansion of copper. This causes the aluminum tocold flow out of the joint or 'connectorthereby decreasing thecrosssectional area of the conductor strip. Also, the cooling down ofthe conductor due to a reduced current flow or due to the reduction ofthe environmental temperature causes the aluminum to retract from theconnector thereby increasing the electrical resistance of theconnection. Once the joint has loosened as a result of cold flow,surface contact resistance between the various components of theelectricaljoint increases both due to a laclt of joint pressure andformation of nonconductive oxides, the oxides developing on the aluminumas a result of the relatively loose fit of the joints or connectorassembly. This increased electrical resistance increases the contactheating during subsequent electrical loading and the thermal cyclingbecomes more destructive until a thermal runaway condition occurs. Whenthis runaway condition occurs the connection fails. I

Another phenomenon occurs with certain connections heretofore used inconnection with the termination of secondary conductors of atransformer, this With the connector assembly of the present invention,all of the problems described above are substantially reduced plusadding other desirable features to the connection of an aluminumterminal strip of the secondary transformer to an external connector.The assembly of the present invention includes the provision of aconcentrically grooved washer, either grooved on one or both faces, thewasher being extremely flat relative to its diameter, and a clampingmechanism is provided for initially slightly deforming or cold flowingthe aluminum by forcing the. concentrically grooved face of the washerslightly into the surface of the aluminum buss bar strip. In this way,any aluminum oxide crust that may be present on the face of the aluminumbuss bar is broken thereby providing intimate contact between theexposed clean surfaces of the aluminum and the sharp ridges of thewasher face. Also, the aluminum is slightly cold flowed into the groovesof the concentrically grooved washer leaving small voids or spaces atthe apex of the void area formed by the grooves in the washer. Thus,when the joint is thermally cycled, the aluminum tends to flow into thevoids formed by the concentric grooves rather than out of the joint tosubstantially limit clamping pressures on the aluminum buss strip.Further, when the joint cools, and the aluminum shrinks at a rategreater than other components in the system, the aluminum is restrictedto movement along the angular faces of the grooves of the concentricallygrooved washer effectively maintaining intimate contact of cleanelectrically conductive surfaces of the aluminum and the washer and alsoessentially maintaining clamping pressure on the joint. Thus, a goodelectrical connection is maintained and the formation of additionalaluminum oxide is precluded.

Accordingly, it is one object of the present invention to provide animproved connector assembly for use in connecting low voltage aluminumstrip conductors to the through connection in a transformer.

It is another object of the present invention to provide an improvedconnector assembly for a transformer which has improved thermal cyclingcharacteristics.

It is a further object of the present invention to provide an improvedconnector assembly for a transformer which precludes oxides from formingin the strip buss connector joint which would be detrimental to theperformance of the connection.

It is still a further object of the present invention to provide animproved connector assembly which enables the effective use of aluminumstrip conductors in the secondary circuit of a transformer.

It is still a further object of the present invention to provide animproved connector assembly for the secondary circuit of a transformerwhich minimizes the resistance of the of the connection throughout thelife of the transformer.

It is still a further object of the present invention to provide animproved connector assembly which is particularly adaptable for use inconnection with interconnecting the secondary winding of a transformerwith the transformer tank exterior conductor.

It is still a further object of the present invention to provide animproved connector assembly for use in conjunction with interconnectingconductors fabricated of materials which have widely varied thermalexpansion characteristics.

It is a further object of the present invention to provide improvedconnector assembly for a transformer which is inexpensive tomanufacture, reliable in use and substantially reduces problemsheretofore encountered in connector assemblies of this type.

Further objects, features and advantages of this invention will becomemore apparent from a consideration of the following description, theappended claims and the accompanying drawings in which:

FIG. 1 is a sectional view of a transformer assembly, illustrating theprimary and secondary windings in symbolic form, and particularlyillustrating the connector assembly of the present invention;

FIG. 2 is a plan view of a grooved washer of the present invention;

FIG. 3ais a cross-sectional view of the washer of FIG. 2 taken alonglines Zia-3a thereof;

FIG. 3b is a cross-sectional view of a modified form of washer of FIGS.2 and 3a and particularly illustrating grooving on both faces of thewasher;

FIG. 4 is a detail view of a connector assembly of the present inventionand particularly illustrating two single faced grooved washers on eitherside of a buss bar;

FIG. 5 is a perspective view of a laminated buss bar and particularlyillustrating the edge welding thereof;

FIG. 6 is aside view of the connector assembly of FIG. 4 andparticularly illustrating the use thereof in connection with thelaminated buss bar of FIG. 5; and

FIG. 7 is a side view of a modified connector assembly and particularlyillustrating the use of two single face groove washers on the outboardsides oflaminated buss bars and further including adouble faced groovedwasher between selected laminations of the buss bars or between twolaminated buss bars terminating to one threaded stud connectionassembly.-

Referring now to the drawings, and particularly to FIG. 1 thereof, thereis illustrated a transformer assembly 10 which is formed generally of anouter casing 12 and a cover member 14, as is typical in the art. Theprimary conductors of the transformer are fed a high voltage by means ofan input conductor assembly 16 which includes an insulating member 18 toinsure that the high voltage is isolated from the tank. The high voltageis fed to the primary winding, symbolically illustrated at 20, by meansof conductors 22,24 and the primary is magnetically coupled with asecondary winding, symbolically illustrated at 26.

The interior of the transformer tank 12 is filled with oil generally toa level indicated at 28 to provide a cooling and insulating fluid forthe transformer windings 20,26. The cover member 14 is joined to themain tank at a lip section, a lip being formed on both the tank and thecover at 30,32, respectively. The two lips are joined by means of a clip34 or other similar type of fastening member commonly used intransformers of this type.

The secondary winding 26 includes a pair of output conductors, one ofwhich is symbolically illustrated at 36, and the other of which isillustrated as a strip or bar conductor assembly 38. It is to beunderstood that both the output conductors 36,38 are identical. Theconductor 38 is fed through the transformer tank wall 12 by means of aconnector assembly 40, forming at least a portion of the subject matterof the present invention.

The connector assembly 40 includes means for hermetically sealing theinterior of the connector assembly 40 such that the oil 28 does not leakto the exterior of the tank 12. Typically, a pair of cup elements 42,44form this sea] and the connection is made through the interior of thecup members 42,44. In the case of the present invention, the busselement 38 is connected to a stud member 46 by meansof a plurality oflocknuts and washers to be more fully explained in conjunction with thedescription of FIGS. 2 through 7. The stud member 46 extends through theinterior of the cup elements 42,44 to an exterior connector 50 to whichthe service conductors are connected.

As was stated above, it has been found that aluminum conductors, formedas is conductor 38, may be effectively used in conjunction with thesecondary windings of a transformer if the problems of oxidation andthermal cycling at the lead terminations are solved. It has been foundthat both of these problems may be substantially reduced by the use of aconcentrically grooved washer interposed between the strip conductor anda fastening member, as for example a nut. Such a washer element isillustrated at 54 in FIG. 2. The washer element includes a centrallylocated aperture 56 and a plurality of grooves 58 formed therein. It hasbeen found that the grooves may be easily formed in the washer 54 bymounting the washer on a mandrel and rotating the washer in a positionadjacent a sharp. cutting tool thereby cutting the grooves in the washerrather than applying the grooves by means of a stamping process. It hasbeen found that the grooves could best be applied by the use of a taptool, the tap being positioned with the axis of the tool parallel to theface of the washer, for simultaneous cutting of plural grooves. Theoperating edge of the flute of the tap actually inachines the grooves.

FIGS. 3a and 3b illustrate a cross-sectional view of washers which maybe typically used in connection with connector assemblies incorporatingfeatures of the present invention. Particularly, FIG. 3a is acrosssectional view of a washer having a grooved area on a single facesuch as that illustrated in FIG. 2. FIG. 3b is a modified form of awasher 60 having the identical inner aperture62 as was described inconjunction with FIGS. 2 and 3a and a plurality of grooves 64 on oneface of the washer 60. Additionally, the washer 60 is provided with asecond set of concentric grooves 66 on the opposite face of the washer60. Thus, the washer 60 may be utilized in conjunction with two aluminumconductor strips, the washer being positioned between the two stripssuch as will be described in conjunction with FIG. 7.

Referring now to FIG. 4, there is illustrated a typical connectorassembly utilizing the principles of the present invention.Particularly, the connector assembly is associated with a transformertank 12 including the cup member 42 described in conjunction withFIG. 1. A buss bar assembly is illustrated at 38 and includes aninsulating tube and central conductor 70. The buss strip 70 is insertedon the stud 46 after a nut 78 and a single faced washer 54 is insertedon the stud 46.

Thereafter, a second single faced concentric washer 54 is applied withthe grooves in the case of both washers facing the buss conductor 70.Finally, a compression nut 80 and a locknut 82 are applied, thecompression nut 80 compressing the assembly, including the washers 54and conductor 70, to cause the aluminum conductor 70 to cold-flow sothat aluminum is forced into the grooves 58 to a certain extent.However, the grooves are not completely filled and a void is provided.The nut 82 is then applied to lock the assembly in the position shown.

Referring now to FIGS. 5 and 6, there is illustrated a modified form ofthe conductor 70, the modified form being fabricated as a laminated bussassembly 86. The conductor 86 of FIG. 6 is fabricated as illustrated inFIG. 5. Particularly, the conductor 86 is fabricated of aluminumstripswhich are'placed in face abutting relation and tig welded, as at 88, toinsure that all the individual conductors are provided with a goodelectrically conductive path to the faces of the concentric groovedwasher connectors. The weld 88 is made close to an aperture 90 to reducethe electrical path. The aperture 90 is utilized to permit insertion ofthe stud member 46. The assembly of. FIG. 6 is seen to be sub stantiallyidentical to that described in conjunction with FIG. 4 with theexception of the type of conductor 86 being connected to the stud .46.As was the case above, the connector assembly includes a nut 78, asingle face grooved washer 54, a second single face grooved washer 54, acompression nut 80 and a locknut 82. The connector assembly is puttogether identically to that described in conjunction with FIG. 4.

Referring now to FIG. 7, there is illustrated a further modified form ofconductor assembly 92, this assembly being formed of afirst and secondlaminated conductor assemblies 94,96, each laminated conductor 94,96being tig welded as wasthe case with conductor 86. Again, theexteriorassembly of the conductor assemblies92 is identical to that described inconjunction with FIGS. 4 and 6 and includes a nut 78, a pair of sin gleface grooved washers 54, a compression nut 80 and a locknut 82 to fastenthe entire assembly on a stud46. However, a space is provided betweenconductor assemblies 94,96 into which is inserted a double face groovedwasher 60 such as was described in conjunction with the description ofFIG. 3b. The washer 60 includes the two grooved faces into which thealuminum of the conductors 94,96 are cold-flowed as a result of theturning of the compression nut 80. The washer 60 is provided to increasethe electrical contact between conductors 94,96, and thus maintain goodelectrical conductivity between conductor assemblies 94 and 96.

Accordingly, when any of the connections illustrated in FIGS. 4, 6 or 7are thermally cycled, the difference in expansion and contraction of thevarious materials used in the connector assembly, for example copper,brass and aluminum, will cause a differential expansion and an increasein the compressive force on the washer and conductor assembly. This willcause the aluminum to flow into the grooves or the voids created by thegrooves and subsequent reduction in temperature will permit the aluminumto remain in contact with the grooved faces of the washer therebymaintaining the electrical contact. It is preferable to fabricate thewashers such that the grooved washer faces will have quite sharp ridgesto allow ready penetration into the aluminum strip surface. It has beenfound that the thermal cycling characteristics are improved with asharper washer. I

While it will be apparent that the preferred embodi ments of theinvention disclosed are well calculated to fulfill the objects abovestated, it will be appreciated that the invention is susceptible tomodification, variation and change without departing from the propermaterial, and means for maintaining the electrical resistance of theconnector assembly after the connector assembly has been thermallycycled including a washer having a plurality of concentric groovesformed on at least one fact thereof, said washer being positioned on thestud adjacent the said soft material between two compression elementswith the said grooves being con-- tiguous with the soft material, thecompression elements being operated toforce soft material at leastpartially into said grooves. I

2. The improvement of claim 1 wherein said at least one of the windingsis the secondary winding and said ends are fabricated of aluminum, saidgrooves being formed with sharp ridges and are continuous.

3. The improvement of claim 2 wherein the circuit to the exterior of thetransformer tank includes said aluminum ends, said washer, saidcompression element and the stud.

'4. In the transformer assembly of claim 2 further including coolingfluid contained within the tank, the improvement further comprising saidconnector assembly having at least a portion thereof within the tank andbelow the level of said cooling fluid and further including means forproviding afluid-tightseal with the tank.

5. The improvement of claim 3 wherein said ends are fabricated of aplurality of aluminum strips, said aluminum strips including an apertureformed adjacent one end thereof.

6. The improvement of claim 5 wherein said aluminum strips arepositioned in face to face abutting relation and a weld is provided atthe edges of said strips closely adjacent said aperture to maintain theelectrical resistance characteristics of said welded strips.

7. The improvement of claim 6 wherein said connector assembly includes asecond washer having a concentrically grooved face, said second washerbeing positioned adjacent said aluminum strips with said grooved facecontiguous with said aluminum strips.

8 The improvement of claim 7 wherein said compression element operatesto force soft material at least partially into the said grooves of saidsecond washer.

9. The improvement of claim 8 wherein said weld is discontinuous acrossthe edges of said aluminum strips, at least two of said strips beingspaced at said discontinuity to provide a space between said strips.

10. The improvement of claim 9 .wherein said connector assembly furtherincludes a third washer positioned in said space between said strips,said third washer having concentrically grooved faces on opposite sidesof said washer, said compression element operating to force softmaterial at least partially into said grooves of said third washer.

11. The method of forming a transformer assembly comprising the steps ofassembling a primary winding and a secondary winding in a tank,assembling a connector assembly including a stud associated with atleast one of said windings, the ends of the at least one of the windingsbeing fabricated of a soft, cold-flowable material, and maintaining theelectrical resistance of the connector assembly after the assembly hasbeen thermally cycled including assembling a washer with a plurality ofconcentric grooves on at least one face of said washer, positioning atleast two compression elements and the said washer on the stud adjacentthe soft material, said washer being between the two compressionelements with said groove being positioned contiguous with said softmaterial, and operating at least one compression element to force saidsoft material at least partially into said grooves.

12. In the transformer assembly of claim 11 wherein at least one of thesaid windings is the secondary winding and said ends are fabricated ofaluminum.

13. In the transformer assembly of claim 12 wherein the circuit to theexteriorof the transformer tank includes said aluminum ends, saidwasher, said compression elements andthe stud.

14. In the transformer assembly of claim 12 further including coolingfluid contained within the tank, the

into said grooves of said third washer.

one end thereof.

16. The method of claim 15 further including positioning said strips inface to face abutting relation and welding the edges of said stripsclosely adjacent said aperture to maintain the electrical resistancecharacteristics of said welded strips.

17. The method of claim 16 further including providing a second washerhaving a concentrically grooved face, and positioning said second washeradjacent said aluminum strips with said grooved face contiguous withsaid aluminum strips.

18. The method of claim 17 further including operating said compressionelement to force soft material at least partially into the said groovesof said second washer.

' 19. The method of claim 18 further including providing a discontinuityacross the edges of said aluminum strips, and spacing at least two ofsaid strips at said discontinuity to provide a space therebetween.

20. The method of claim 19 further including providing a third washer insaid space between said strips, said third washer having concentricallygrooved faces on opposite sides of said washer and operating saidcompression element to force soft material at least partially 21. Theimprovement of claim 11 wherein at least two of said washer, stud andcompression elements are of differing coefficients of thermal expansion.

22. The method of claim 11 wherein said washer is formed by stepsincluding mounting blank washer stock on a mandrel, mounting a cuttingtool adjacenta face of the washer stock, rotating one of said stock andtool relative to the other, and advancing one of said stock and toolrelative to the other.

2. The improvement of claim 1 wherein said at least one of the windingsis the secondary winding and said ends are fabricated of aluminum, saidgrooves being formed with sharp ridges and are continuous.
 3. Theimprovement of claim 2 wherein the circuit to the Exterior of thetransformer tank includes said aluminum ends, said washer, saidcompression element and the stud.
 4. In the transformer assembly ofclaim 2 further including cooling fluid contained within the tank, theimprovement further comprising said connector assembly having at least aportion thereof within the tank and below the level of said coolingfluid and further including means for providing a fluid-tight seal withthe tank.
 5. The improvement of claim 3 wherein said ends are fabricatedof a plurality of aluminum strips, said aluminum strips including anaperture formed adjacent one end thereof.
 6. The improvement of claim 5wherein said aluminum strips are positioned in face to face abuttingrelation and a weld is provided at the edges of said strips closelyadjacent said aperture to maintain the electrical resistancecharacteristics of said welded strips.
 7. The improvement of claim 6wherein said connector assembly includes a second washer having aconcentrically grooved face, said second washer being positionedadjacent said aluminum strips with said grooved face contiguous withsaid aluminum strips. 8 The improvement of claim 7 wherein saidcompression element operates to force soft material at least partiallyinto the said grooves of said second washer.
 9. The improvement of claim8 wherein said weld is discontinuous across the edges of said aluminumstrips, at least two of said strips being spaced at said discontinuityto provide a space between said strips.
 10. The improvement of claim 9wherein said connector assembly further includes a third washerpositioned in said space between said strips, said third washer havingconcentrically grooved faces on opposite sides of said washer, saidcompression element operating to force soft material at least partiallyinto said grooves of said third washer.
 11. The method of forming atransformer assembly comprising the steps of assembling a primarywinding and a secondary winding in a tank, assembling a connectorassembly including a stud associated with at least one of said windings,the ends of the at least one of the windings being fabricated of a soft,cold-flowable material, and maintaining the electrical resistance of theconnector assembly after the assembly has been thermally cycledincluding assembling a washer with a plurality of concentric grooves onat least one face of said washer, positioning at least two compressionelements and the said washer on the stud adjacent the soft material,said washer being between the two compression elements with said groovebeing positioned contiguous with said soft material, and operating atleast one compression element to force said soft material at leastpartially into said grooves.
 12. In the transformer assembly of claim 11wherein at least one of the said windings is the secondary winding andsaid ends are fabricated of aluminum.
 13. In the transformer assembly ofclaim 12 wherein the circuit to the exterior of the transformer tankincludes said aluminum ends, said washer, said compression elements andthe stud.
 14. In the transformer assembly of claim 12 further includingcooling fluid contained within the tank, the method further comprisingsaid connector assembly having at least a portion thereof within thetank and below the level of said cooling fluid and further providing afluid-tight seal with the tank.
 15. The method of claim 13 furtherincluding fabricating said ends of a plurality of aluminum strips, andforming an aperture in said aluminum strips adjacent one end thereof.16. The method of claim 15 further including positioning said strips inface to face abutting relation and welding the edges of said stripsclosely adjacent said aperture to maintain the electrical resistancecharacteristics of said welded strips.
 17. The method of claim 16further including providing a second washer having a concentricallygrooved face, and positioning said second washer adjacent said aluminumstrips with said grooved face Contiguous with said aluminum strips. 18.The method of claim 17 further including operating said compressionelement to force soft material at least partially into the said groovesof said second washer.
 19. The method of claim 18 further includingproviding a discontinuity across the edges of said aluminum strips, andspacing at least two of said strips at said discontinuity to provide aspace therebetween.
 20. The method of claim 19 further includingproviding a third washer in said space between said strips, said thirdwasher having concentrically grooved faces on opposite sides of saidwasher and operating said compression element to force soft material atleast partially into said grooves of said third washer.
 21. Theimprovement of claim 11 wherein at least two of said washer, stud andcompression elements are of differing coefficients of thermal expansion.22. The method of claim 11 wherein said washer is formed by stepsincluding mounting blank washer stock on a mandrel, mounting a cuttingtool adjacent a face of the washer stock, rotating one of said stock andtool relative to the other, and advancing one of said stock and toolrelative to the other.